The problem was fixed yesterday within hours of it being noticed, according to a statement from Symantec, which acquired Norton and its antivirus software a decade ago. "The issue occurred due to content within the site being falsely identified as a phishing risk," the company said.

"We are aware that some Norton customers encountered a security warning page when attempting to access the Facebook Web site," Symantec said in a statement. "Norton has corrected this issue and delivered a fix via LiveUpdate, which will be downloaded automatically and will resolve the issue. Customers can also run LiveUpdate manually from the main user interface of their Norton product to ensure they have the latest updates."

The problem affected a subset of Norton Internet Security and Norton 360 customers who attempted to access Facebook during a limited window of time, according to Symantec.